Amazon - refuse delivery or return "properly"?

Hi

I ordered the wrong thing on Amazon (mum had sent me a few links!) and can no longer cancel my order.

They've wrote a few options on the email and I was just wondering if it's best to refuse delivery or return via postage label? Does it take longer to refund if I refuse delivery? I've never had to return anything to Amazon so just wanted to ask which is the best/quickest option?

Thanks